This is a small subroutine to convert a decimal IP address to its binary equivalent. The function takes an IP address and an optional delimter to separate the bytes. I am in the process of writing a small tutorial on the basics of TCP/IP networking and I'm using this function to generate examples. It might also be useful for determining CIDR style netmasks (192.168.10.0/24) such as those used by nmap and Apache allow/deny directives with a little work. 

ip2bin('255.255.255.0', ' ')
returns 
11111111 11111111 11111111 00000000

Update:

Another way to do this is to use the inet_aton function in the Socket module. A perl one liner to produce the same output:

perl -MSocket -e 'printf ("%s %s %s %s", unpack('B8B8B8B8', inet_aton('255.255.255.0')))'

Thanks AgentM for the pointer.

sub ip2bin{
    my ($ip, $delimiter) = @_;
    return     join($delimiter,  map 
        substr(unpack("B32",pack("N",$_)),-8), 
        split(/\./,$ip));
}

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In reply to Converting decimal IP addresses to binary by Coyote

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